Could somebody has any idea about why I can't see he Exposure Compensation function (+/-) changes in Live View window in Manual mod but in the other mods (P,S,A) it does....? I press the exposure compensation buton, see how the (- or +) changes in the visible bar at button of the Live View window, but the scene doesn't darks or brights. Any idea? Thanks to all.

because there is no compensation. if you don't expose properly the camera considers it your choice. if you want to expose correctly you will need to expose correctly. this is easily achived using aperture, shutter speed and ISO.

saultv - if You in manual mode than it's You who chooses the exposure, therefore there's no need to use the compensation function, for me that's logical, if You set 1/25 than that's what You want, if You want to shift in either way, You just adjust Your setting, that's why it's called manual. In other modes, You don't have this option as either one or both (S and A) are chosen by the camera, therefore using compensation function is necessary to adjust the shutter speed as changing either S or A will also give a different value to the A or S respectively.

each full stop lets in double the light of the previous stop. in terms os shutter speed, this means that 1/125 lets in twice the light of 1/250 (if the light is continuous) and f/2.8 lets in twice the light of f/4 and ISO400 lets in twice the light of ISO200.

open your eyes for twice as long (shutter speed) and they absorb twice the amount of light (if the light remains constant over the period your eyes are open)

open your eyes twice as wide (aperture) and they absorb twice the amount of light (regardless of light levels and duration)

take some mushrooms (ISO) and you can see things no one else can (regardless of light levels and duration)

Exposure compensation does work in M mode, but like Adam and Gareth are saying, it mostly works to confuse you.

What you're doing is changing where the camera is going to tell you it thinks proper exposure is. So, if for the scene you're looking at 1/100 s and f/4 is where it thinks you're getting the right amount of light for that particular scene, adding +1 EV (one stop) of exposure compensation will make the exposure meter tell you that your shot is underexposed at 1/100s and f/4. To get it to zero, you'll have to change your shutter speed, aperture, or ISO.

I personally wouldn't touch the exposure compensation while you're in M mode, though. If you're somewhere like on a beach or in snow and you know you want a stop or two more light than the camera will suggest, you just think about adjusting your exposure until the meter is a stop or two above 0 EV.

Gareth said:
take some mushrooms (ISO) and you can see things no one else can (regardless of light levels and duration)